Fix odd tag indentation by remove list wrapper

* Create a tag list as per the style guide
Use a form with hidden fields to submit tags

* Avoid using inline javascript to submit form
* Based on pattern used by new_url form
* Pre-fill tag filter form with any tags already being filtered by
Add tag field label
Refer to tags as "All tags" in filter field
Style select2 correctly when in an input-group

* Bootstrap 3 styles don’t reset the rounded corners of the select2
list element